Paul Bourassa

Characterization of Dynamic Vehicle Stability Using Two Models of the Human Pilot Behaviour

SUMMARY This article deals with a study of the stability of the vehicle/pilot system for two different models of human operator behaviour. These models, are the outcome of various.approximations of the precision model for single loop compensatory situations. The vehicle is represented with two degrees of freedom and the pilot is assumed to respond to the lateral displacement and to the lateral velocity with a time delay. The properties of these resulting systems are presented and it is observed that, for any given forward visibility, a critical velocity defines a domain of controllability from a domain of uncontrollability. Furthermore this critical velocity is shown independant of the vehicle/ pilot parameters and may be considered as a possible vehicle safety criterion.

Nonlinear oscillations and chaotic motions in a road vehicle system with driver steering control

The nonlinear dynamics of a differential system describing the motion of a vehicle driven by a pilot is examined. In a first step, the stability of the system near the critical speed is analyzed by the bifurcation method in order to characterize its behavior after a loss of stability. It is shown that a Hopf bifurcation takes place, the stability of limit cycles depending mainly on the vehicle and pilot model parameters. In a second step, the front wheels of the vehicle are assumed to be subjected to a periodic disturbance. Chaotic and hyperchaotic motions are found to occur for some range of the speed parameter. Numerical simulations, such as bifurcation diagrams, Poincaré maps, Fourier spectrums, projection of trajectories, and Lyapunov exponents are used to establish the existence of chaotic attractors. Multiple attractors may coexist for some values of the speed, and basins of attraction for such attractors are shown to have fractal geometries.

Evaluation of the lambda model for human postural control during ankle strategy

Abstract.An accurate modeling of human stance might be helpful in assessing postural deficit. The objective of this article is to validate a mathematical postural control model for quiet standing posture. The postural dynamics is modeled in the sagittal plane as an inverted pendulum with torque applied at the ankle joint. The torque control system is represented by the physiological lambda model. Two neurophysiological command variables of the central nervous system, designated λ and μ, establish the dynamic threshold muscle at which motoneuron recruitment begins. Kinematic data and electromyographic signals were collected on four young males in order to measure small voluntary sway and quiet standing posture. Validation of the mathematical model was achieved through comparison of the experimental and simulated results. The mathematical model allows computation of the unmeasurable neurophysiological commands λ and μ that control the equilibrium position and stability. Furthermore, with the model it is possible to conclude that low-amplitude body sway during quiet stance is commanded by the central nervous system.

Vehicle/Pilot System Analysis: A New Approach Using Optimal Control With Delay

SUMMARY This article deals with the simulation of a vehicle/pilot system experiencing external disturbances. In the simulation, the car is modeled with two degrees of freedom and the pilot is assumed to respond to the state vector with a time delay. When perturbations are introduced, the pilot is expected to drive his car back to the initial state while minimizing a quadratic cost function. With some simplifications for low frequencies responses, the model is then used to simulate the response of different vehicles to an initial step in lateral displacement. The results from the simulations are interpreted in the light of the controllability diagrams.

Intermittent Predictive Steering Control as an Automobile Driver Model

The originality of this paper is the evaluation of intermittent control as a viable candidate to represent an automobile driver in a path tracking scenario. The control algorithm is based on general predictive control where the road curvature is considered known for a horizon in front of the automobile. The computed steering wheel command is used in an intermittent fashion, the intermittence period being one of the system parameter to study. Simulations are carried out and parameters of the driver, the automobile, and the road are varied. An intermittence period range giving satisfactory performances is observed. A comparison is made with actual car/driver behavior measurements for a lane change maneuver. It is concluded that, according to this driver model, there is a wide range of intermittence period that the automobile driver may be operating. Moreover, it is suggested to consider the intermittency of information as an important parameter for vehicle safety systems.

On the Extension of the Gratzmuller Critical Velocity for Locked Steering Road Vehicle to the Case of Piloted Vehicles

SUMMARY This study deals with the stability of a vehicle/pilot system in which the pilot mathematical model is derived from a single-loop general model and is characterized by a set of four parameters involving a loop gain constant K, a phase-lead time Ta, a pure time delay τ, and a neuromuscular lag-time constant Tr. The vehicle model consist of a two degrees of freedom model in yaw ψ and lateral displacement y. The properties of the coupled system are then studied and the existence of a maximum control velocity u as a function of the pilot longitudinal visibility L is demonstrated. This velocity is seen to be independant of the pilot interaction parameter and may serve as a safety criterion for a given vehicle. Finally, the effect of the stiffness of the rear and front tires upon the critical velocity is evaluated and it is shown that as the visibility L becomes infinite, this velocity expression coincides with the one proposed by Gratzmuller in the context of a fixed steering road vehicle.

Influence d'un poids lourd équipé ou non de dispositifs aérodynamiques sur une automobile en manoeuvre de dépassement

Abstract Dynamic wind-tunnel tests of the overtaking manoeuvre between a tractor—trailer truck and a tourist car have been carried out in order to determine the effects of a drag-reduction deflector and the lateral skirts on the aerodynamic characteristics of the car.

CONTROL OF THE SIMPLEST WALKING MODEL WITH LAMBDA MODEL

Abstract The analysis of the simplest biped walking machine can provide much insight into dynamics and control of human gait. The problem, in the sagittal plane, consists to control the impulse force under the swing foot and the torque between the legs in order to reach a stable limit cycle. The main contribution of this paper concerns the hierarchical control based on the physiological Lambda model and a pattern generator working with intermittent data. The feedback is tuned in order to obtain oscillations at the walking frequency. Simulation results present stable limit cycle.

Nonlinear Lateral and Yaw Dynamics and Stability of Snow mobiles

SUMMARY This paper takes a close look at the mechanism of locomation in snowmobiles. A mathematical model is developed taking into account the inherent nonlinearities of the system. A piece-wise linear approach is presented. A nonlinear methodology is used to construct stability maps for the yaw dynamics. The strategy can be extended to assess the stability in lateral slip of the snowmobile when negotiating a turn. The developed models and strategies are useful design tools for a wide class of snowmobiles.

Time-scaling Control of a Compass Type Biped Robot

This paper presents a robust control strategy driving an actuated compass gait robot towards steady gaits. The originality lies in the generation of the swing leg references as a simple function of the supporting leg angle. Simulations and experimentation showed that the system exhibits asymptotically stable walking cycles with large and strong basins of attraction.